1. Field of the Invention
The present invention relates to an optical switch whereby an optical signal that is input to any one of a plurality of input ports is output at any one of a plurality of output ports.
2. Description of Related Art
Prior art optical switches are disclosed in Reference 1 “Proceedings of the 3rd International Conference on Micro Opt Electro Mechanical Systems (MOEMS 99), Paper 26, Aug. 29, 1999”, Reference 2 “U.S. Pat. No. 5,923,480, Jul. 13, 1999”, Reference 3 “Laid-open Japanese Patent Publication No. 2000-10029” and Reference 4 “Optical Fiber Communication (OFC) 2000 Collected Papers, Paper PD 20, March 2000”.
As an example of a prior art optical switch, the optical switch described in Reference 3: Laid-open Japanese Patent Publication No. 2000-10029 is illustrated in FIG. 44.
FIG. 44(A) is a diagram of the layout of this prior art optical switch 4400. This optical switch 4400 comprises several optical deflection elements 4402 (4402a, 4402b) and a mirror 4404.
Mirror 4404 is fixed in a prescribed position within optical switch 4400. Also, optical deflection elements 4402 are aligned and arranged on a substrate 4406 facing this mirror 4404, separated by a space.
The optical and deflection elements 4402 (4402a, 4402b) referred to above are respectively provided with optical input/output ports. The terminal sections of optical fibers 4408 (4408a, 4408b) are inserted into these optical input/output ports and, furthermore, these terminal sections are inserted into optical deflection elements 4402, and fixed in the interior thereof.
Next, the operation in an optical switch 4400 constructed as above will be described. In this optical switch 4400, input and output of light are performed simultaneously by respective optical input/output ports.
Light that is emitted from the terminal section of optical fiber 4408b is input to optical deflection element 4402b, where it is deflected. After this, light emitted from optical deflection element 4402b is reflected by mirror 4404 and again input to optical deflection element 4402a. It is then guided into optical fiber 4408a by this optical deflection element 4402a, and output from an optical input/output port.
Next, the construction of an optical deflection element 4402 is shown in FIG. 44(B). In this optical deflection element 4402, there are arranged optical fiber 4408 inserted from the optical input/output port, collimator lens 4410, fixed mirror 4412, and moveable mirror 4414.
The light that is input from the optical input/output port is output from the terminal section of optical fiber 4408 within optical deflection element 4402. This light is collimated by collimator lens 4410, reflected by fixed mirror 4412, and deflected in the direction of moveable mirror 4414. It is then reflected with a deflection angle that may be chosen at will at this moveable mirror 4414.
This moveable mirror 4414 is moveable biaxially, having an axis of rotation perpendicular to the direction of incidence of the light. Adjustment of the rotation of moveable mirror 4414 is performed using any desired means.
The light can therefore be reflected towards mirror 4404 (FIG. 44(A)) with any desired deflection angle at this moveable mirror 4414. The light is then emitted via mirror 4404 in the direction of a prescribed optical deflection element 4402a. 
In contrast, light that is again input to optical deflection element 4402a advances in the opposite direction to the direction of the arrow shown in FIG. 44(B) and is deflected by moveable mirror 4414. After this, the light is reflected by fixed mirror 4412, collimated by collimator lens 4410, input into optical fiber 4408a, and output from the input/output port. In this case, adjustment of the angle of deflection is performed at moveable mirror 4414 in order to input the light into optical fiber 4408a. 
As described above, an optical switch of this type is constituted by a single-stage group of optical deflection elements, respectively moveable mirrors or moveable lenses being employed for these. The optical signal is then directed to a prescribed output port by controlling the direction of the light beam propagated through the space using a moveable mirror (or moveable lens). With such an optical switch, expansion of the number of ports is easy, since three-dimensional spatial “path arrangement” is employed.
However, in a conventional optical switch, setting of the angle of deflection of the light beam that is propagated through the space must be performed with fairly high accuracy with a single deflection element. Also, as described below, achievement of this accuracy is extremely difficult.
The diameter of the optical fibers that are employed in an ordinary optical communication system is of the order of 8 micron. Unless the light is input to the optical fiber with a position offset accuracy of the order of one micron, loss of one dB or more is produced, causing problems in practical use. An output port separation of at least a few hundred microns is considered to be necessary in practical installation, so even in the case of a two-channel device, the deflection angle needs to be accurate to of the order of 0.1%. Furthermore, in the case of a device having a few tens of channels, accuracy of the level 10−4 is required.
Also, in the case of a hundred-channel device using a moveable mirror, accuracy of the deflection angle of the order of 1% is considered necessary. And in the case of a device of 1000 or more channels, accuracy of 0.3% is demanded.
Previously, as a method of solving this problem, the method is known of superimposing the position detection signal on the light beam so that the angle of deflection can be detected and feeding back the detected angle to the deflection angle control system. However, with this method, there is the drawback that high-speed switching cannot be performed, because of considerations involving the speed of electrical processing. The method is also known of incorporating an angle detection mechanism in the deflection mirror and controlling this by feedback, but it has the drawback that high accuracy is not obtained.
An object of the present invention is to alleviate the accuracy that is required for the optical deflection elements provided in an optical switch.
Also, a further object of the present invention is to increase the number of channels and to perform optical switching at high speed.